BIO150Y: Evolution of Cooperation Evolutionary Game

Tit for Tat in Nature
Examples of cooperative behaviour in which individuals
appear to be using Tit for Tat

Does Tit for Tat work in nature?
Theoretically you have seen how a rule as simple as Tit for Tat may result in cooperation among selfish individuals in interactions such as Prisoner's Dilemma game. Could individuals in the real world be using Tit for Tat in social interactions? There is debate over how important or prevalent Tit for Tat might be in nature, but there is evidence it is used in the following examples of social behaviour.

Predator inspection
When a group of guppies moves into a new area, two fish will swim out side by side from the group to check for predators. Then one will move ahead one or two body lengths towards the predator for a closer look. The other will cooperate and move forward to take the lead. In this way, the pair will "leap-frog" out until they have checked that the area is clear for the rest of the group to follow.

Blood sharing
On any given night, not all vampire bats get a feed of blood. The lucky bats often get more than enough, while the unlucky ones run the risk of starving. In addition to sharing some of their blood meal with relatives, it has been shown experimentally that well-fed bats will donate blood to hungry bats who roost near them and are familiar to them. These individuals are likely ones who in the past have donated their extra blood.

Trench warfare
During World War 1, the British and German armies were often stuck in trenches facing each other, living in terrible conditions. Several times, soldiers on both sides ceased shelling the other side. In effect, a "live and let live" pact developed. Soldiers would pretend to fight but would aim to miss. Occasional deadly force would be met with instant retaliation, but each side would quickly forgive transgressions. In some cases, the generals had to send in new recruits to break up the pacts that had developed.
Further information
If you would like to read more about these fascinating examples of Tit for Tat in nature, references to good articles are given in the bibliography.

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